1. Field of the Invention
The present invention relates to a Liquid Crystal Display (LCD) device, and more particularly, to a local dimming driving method and device of an LCD device, which is capable of compensating for a luminance deviation between blocks.
2. Discussion of the Related Art
Recently, as an image display device, a flat panel display device such as a Liquid Crystal Display (LCD) device, a Plasma Display Panel (PDP) device, or an Organic Light Emitting Diode (OLED) device is mainly used.
An LCD device includes a liquid crystal panel for displaying an image using a pixel matrix using electrical and optical characteristics of liquid crystal with anisotropy of a refractive index and a dielectric constant, a driving circuit for driving the liquid crystal panel, and a backlight unit for irradiating light to the liquid crystal panel. Each pixel of the LCD device expresses gray scale, by changing a liquid crystal arrangement direction according to a data signal so as to control transmittance of light from the backlight unit through the liquid crystal panel and a polarization plate.
In the LCD device, the luminance of each pixel is determined by a product of the luminance of the backlight unit and light transmittance of liquid crystal according to data. The LCD device uses a backlight dimming method for analyzing an input image, controlling a dimming value so as to control the luminance of the backlight unit and compensating data, in order to improve a contrast ratio and reduce power consumption. For example, a backlight dimming method for reducing power consumption decreases the luminance of the backlight unit by decreasing the dimming value and increases the luminance of the backlight unit by compensating data, thereby reducing power consumption of the backlight unit.
Recently, as a backlight unit, a Light Emitting Diode (LED) backlight unit using an LED as a light source, which has high luminance and low power consumption as compared with existing lamps, is used. Since the LED backlight unit can be controlled according to positions, the LED backlight unit may be driven by a local dimming method of dividing the LED backlight unit into a plurality of light emitting blocks and controlling the luminance of the backlight unit on a block-by-block basis. In the local dimming method, since the backlight unit and a liquid crystal panel are divided into the plurality of blocks, data is analyzed on a block-by-block basis so as to determine a local dimming value, and the data is compensated, it is possible to further improve a contrast ratio and to further reduce power consumption.
Each of the plurality of light emitting blocks of the LED backlight unit includes a plurality of LEDs connected in series. However, in a conventional LED backlight unit, a luminance deviation between blocks occurs due to a characteristic difference between LEDs, an assembly difference between tools, a characteristic difference between optical sheets, or light leakage. Such a luminance deviation between blocks occurs in an edge type backlight unit as well as a direct type backlight unit. In addition, if luminance deviation between blocks is large at the same gray scale, the LCD device may deal with a defect product.